Komatsu PC400LC-6 Fault Code E231: Complete Diagnostic Guide

What is Komatsu PC400LC-6 Fault Code E231?

Fault Code E231 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code specifically relates to the coolant temperature sensor sending irregular voltage signals outside the manufacturer's specified parameters to the ECM.

In the Komatsu PC400LC-6, the coolant temperature sensor plays a critical role in engine management, controlling fuel injection timing, idle speed, and preventing overheating damage. When this sensor fails or sends erratic signals, the ECM cannot properly regulate engine performance, potentially leading to reduced efficiency, increased emissions, or catastrophic engine damage if overheating occurs undetected.

Common Symptoms

When Code E231 is active, operators typically experience:

• Warning light illumination on the instrument panel, specifically the engine or coolant temperature indicator
• Engine derate mode where power output is automatically reduced to protect the engine
• Hard starting or rough idle, particularly when the engine is cold
• Increased fuel consumption due to improper fuel mapping from incorrect temperature readings
• Cooling fan running continuously at high speed, even when engine temperature appears normal

Potential Causes

The most common technical reasons for E231 on used PC400LC-6 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal element breakdown
• Wiring harness damage at known rub points near the engine block or valve cover, common in high-hour machines
• Corroded or loose connector pins at the sensor plug, especially in machines exposed to harsh environments
• ECM internal fault affecting the temperature sensor circuit (less common)
• Damaged sensor ground circuit or poor chassis ground connection
• Coolant contamination causing sensor element coating or failure

How to Troubleshoot and Fix Code E231

Step 1: Visual Inspection Begin by locating the coolant temperature sensor (typically mounted on the engine block or thermostat housing). Inspect the wiring harness for obvious damage, chafing, or burns. On used excavators, pay special attention to areas where harnesses contact metal surfaces or moving components. Check the connector for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult Komatsu specifications). Test the harness continuity from the sensor connector to the ECM. Check for voltage supply at the sensor connector with ignition on—should read approximately 5 volts.

Step 3: Component Replacement and Verification If resistance values are out of specification or the sensor shows physical damage, replace the coolant temperature sensor with a genuine Komatsu part. Before installation, apply dielectric grease to connector pins to prevent future corrosion. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then monitor for code recurrence during operation.

Critical for Used Machines: Always inspect harness routing and secure any loose wiring that may have shifted over time. Replace any brittle or cracked wire insulation common in older machines.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and seek professional assistance from certified technicians for complex repairs or if you're uncertain about any procedure.